#include <bits/stdc++.h>

using namespace std;
#define int long long
const int inf = 0x3f3f3f3f3f3f3f3f;

void solve()
{
	int n, k, x;
	cin >> n >> k >> x;
	vector<string> a(n);
	for (int i = 0; i < n; i++) cin >> a[i];
	vector<string> v;
	if (k == 1)
	{
		for (int b = 0; b < n; b++)
		{
			v.push_back(a[b]);
		}
	}
	else if (k == 2)
	{
		for (int b = 0; b < n; b++)
		{
			string s;
			s += a[b];
			for (int c = 0; c < n; c++)
			{
				s += a[c];
				v.push_back(s);
				for (int x = 0; x < (int)a[c].size(); x++) s.pop_back();
			}
		}
	}
	else if (k == 3)
	{
		for (int b = 0; b < n; b++)
		{
			string s;
			s += a[b];
			for (int c = 0; c < n; c++)
			{
				s += a[c];
				for (int d = 0; d < n; d++)
				{
					s += a[d];
					v.push_back(s);
					for (int x = 0; x < (int)a[d].size(); x++) s.pop_back();
				}
				for (int x = 0; x < (int)a[c].size(); x++) s.pop_back();
			}
		}
	}
	else if (k == 4)
	{
		for (int b = 0; b < n; b++)
		{
			string s;
			s += a[b];
			for (int c = 0; c < n; c++)
			{
				s += a[c];
				for (int d = 0; d < n; d++)
				{
					s += a[d];
					for (int e = 0; e < n; e++)
					{
						s += a[e];
						v.push_back(s);
						for (int x = 0; x < (int)a[e].size(); x++) s.pop_back();
					}
					for (int x = 0; x < (int)a[d].size(); x++) s.pop_back();
				}
				for (int x = 0; x < (int)a[c].size(); x++) s.pop_back();
			}
		}
	}
	else if (k == 5)
	{
		for (int b = 0; b < n; b++)
		{
			string s;
			s += a[b];
			for (int c = 0; c < n; c++)
			{
				s += a[c];
				for (int d = 0; d < n; d++)
				{
					s += a[d];
					for (int e = 0; e < n; e++)
					{
						s += a[e];
						for (int f = 0; f < n; f++)
						{
							s += a[f];
							v.push_back(s);
							for (int x = 0; x < (int)a[f].size(); x++) s.pop_back();
						}
						for (int x = 0; x < (int)a[e].size(); x++) s.pop_back();
					}
					for (int x = 0; x < (int)a[d].size(); x++) s.pop_back();
				}
				for (int x = 0; x < (int)a[c].size(); x++) s.pop_back();
			}
		}
	}
	sort(v.begin(), v.end());
	//cout << v.size() << endl;
	cout << v[x - 1];
}

/*
5 1 1
a
aa
aaa
aa
a
*/

signed main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int _ = 1;
	//cin >> _;
	while (_--)
	{
		solve();
	}
	return 0;
}